Method for transmitting data stream via wireless medium and a wireless network

ABSTRACT

The present invention provides a method for transmitting data stream via wireless medium for contention based medium access across a wireless network having a plurality of stations and an access point communicating to the stations via wireless medium. The method includes: (i) transmitting data stream from the station according to prescheduled wireless medium occupancy reservation for the station within only prescheduled medium occupancy period of a selective contention period; (ii) performing a contention between the stations for wireless medium occupancy for a contention successful station to transmit data stream within only contention medium occupancy period of the selective contention period; (iii) transmitting data stream from the contention successful station after the contention; and (iv) prescheduling a wireless medium occupancy reservation for the contention successful station to transmit within a prescheduled medium occupancy period of next selective contention period.

TECHNICAL FIELD

This invention is to equip a network device with Quality of Service(QoS) awareness system process to serve traffic streams in a coordinatedmanner. This invention also increases QoS awareness and throughputefficiency of traffic streams transmission by coordinating streamtransmission and reduce the number of collision for contention basedmedium access mechanism.

BACKGROUND ART

In prior art, the timing to obtain transmission permit for streamtransmission that is not being coordinated are not base on the streamrequirement. It will try to request for transmission permit without anyother further consideration if the queue is not empty. Furthermore, thepermit is granted based on priority as described in Draft, Supplement toInternational Standard ISO/IEC 8802-11: 1999: ANSI/IEEE Std 802.11, 1999Edition—“Part 11: Wireless LAN Medium Access Control (MAC) and (PHY)Specifications (draft 3.0) and some random periods as described inInternational Standard ISO/IEC 8802-11: 1999: ANSI/IEEE Std 802.11, 1999Edition—“Part 11: Wireless LAN Medium Access Control (MAC) and (PHY)Specifications.

Based on IEEE802.11e Enhanced Distributed Coordination Function (EDCF),the contention for each continuous packets delivery within a particulartime frame causes non-deterministic data packets arrival at the receiverend. Such occurrence of contention is rather prevalent if there is morethan one stream of the same priority are admitted into the Basic ServiceSet (BSS). Contention may occur during each time the station of the samepriority content for medium dedication time. The number of contentionsdepends on the amount of bandwidth allotted to stations and the numberof station within the BSS based on the maximum available bandwidthwithin BSS. Furthermore, the QoS requirement of the transmission streamsis jeopardized when the timing to request for transmission permit is notcoordinated and guarded.

Frequent request for short medium occupancy period leads to highercollisions and overheads. This is especially true when the wirelessstations do not aggregate these short medium occupancy period requestsneeded for delivering data streams from one wireless device to another.

Complicated LSI implementation is required at the network device inorder to preserve the QoS requirement of individual data stream whereeach transmission permit dedication is for plural number of data streamstransmission.

DISCLOSURE OF INVENTION

In accordance with one aspect of the present invention, there is amethod for transmitting data stream via wireless medium for contentionbased medium access across a wireless network having a plurality ofstations and an access point communicating to said stations via wirelessmedium. The method includes:

(i) performing a contention between the stations for wireless mediumoccupancy for a station to transmit data stream at a selectivecontention period;

(ii) transmitting data stream from the contention successful stationafter the contention.

The selective contention period is divided into two distinct period as:

(a) contention medium occupancy period at which the stations contend forwireless medium occupancy for a station to transmit data stream; and

(b) prescheduled medium occupancy period at which a wireless mediumoccupancy reservation for a contention successful station isprescheduled.

In another aspect of the present invention, there is a method fortransmitting data stream via wireless medium for contention based mediumaccess across a wireless network having a plurality of stations and anaccess point communicating to said stations via wireless medium. Themethod includes:

(i) transmitting data stream from the station according to prescheduledwireless medium occupancy reservation for the station withinprescheduled medium occupancy period of a selective contention period;

(ii) performing a contention between the stations for wireless mediumoccupancy for a contention successful station to transmit data streamwithin only contention medium occupancy period of the contentionselective period;

(iii) transmitting data stream from the contention successful stationafter the contention; and

(iv) prescheduling a wireless medium occupancy reservation for thecontention successful station to transmit within a prescheduled mediumoccupancy period of next selective contention period.

Preferably, the access point transmit a beacon signal including aninformation about start period of the contention medium occupancy periodto each station so that selective contention between the stations can beperformed.

It is noted that the beacon signal, the prescheduled medium occupancyperiod, and the contention medium occupancy period may be provided inturn in the selective contention period.

In another aspect of the present invention, when a station is successfulfor a contention at the contention medium occupancy period of theselective contention period, a wireless medium occupancy reservationhaving a duration period for the contention successful station isprescheduled within a prescheduled medium occupancy period of nextselective contention period. Then start period of a contention mediumoccupancy period of next selective contention period is moved forwardfrom the start period of the contention medium occupancy period of theselective contention period by the duration period. It is noted that thestart period of a contention medium occupancy period may be indicated bySelective Contention Backoff Pointer (SCB_Ptr) as shown in FIGS. 2, 4,12A, 13A, 15A, 17A, 19A.

In a further aspect of the present invention, when a first station issuccessful for a first contention at the contention medium occupancyperiod of the selective contention period, subsequently a second stationis successful for a second contention after the first contention, afirst medium occupancy reservation having a first duration period forthe first station is prescheduled within a prescheduled medium occupancyperiod of next selective contention period, subsequently a second mediumoccupancy reservation having a second duration period for the secondstation is prescheduled after the first medium occupancy reservationwithin the prescheduled medium occupancy period of next selectivecontention period. Then start period of a contention medium occupancyperiod of next selective contention period is moved forward from thestart period of the contention medium occupancy period of the selectivecontention period by sum of the first duration period and the secondduration period.

Preferably, the start period and the duration period of transmissionsfrom the first and second stations according to the scheduled wirelessmedium occupancy reservation may be recorded in both the first and thesecond stations.

In a further aspect of the present invention, the station monitorscondition of the wireless medium occupancy in the selective contentionperiod, and records the condition, then transmission timing isdetermined according to the condition of the wireless medium occupancyrecorded.

In a further aspect of the present invention, when the access pointreceives null packet transmitted at the transmission timing according toprescheduled wireless medium occupancy reservation having a durationperiod for the station, the prescheduled wireless medium occupancyreservation will be cancelled, then start period of the contentionmedium occupancy period of next selective contention period will bemoved back by the duration period.

The beacon signal may include information with respect to:

(i) start period and end period of selective contention period havingthe contention medium occupancy period and the prescheduled mediumoccupancy period of the selective contention period; and

(ii) duration period of the selective contention period.

Furthermore, the beacon signal may include information with respect tostart period and duration period of prescheduled wireless mediumoccupancy reservation within the prescheduled medium occupancy period.

In a still further aspect of the present invention, the stationtransmits data stream having last packet including reservation parameterfor wireless medium occupancy reservation having a duration period inprescheduled medium occupancy period of next selective contentionperiod. In addition, the access point receives the reservation parameterincluded in last packet, wireless medium occupancy reservation for thestation will be prescheduled in prescheduled medium occupancy period ofnext selective contention period, then the start period of thecontention medium occupancy period will be moved forward by the durationperiod.

In a yet further aspect of the present invention, there is a wirelessnetwork system comprising a plurality of stations and an access pointcommunicating with the stations via wireless medium.

The access point includes:

-   -   a medium recorder unit which records:        -   (i) start and end period of contention medium occupancy            period in which stations contend for wireless medium            occupancy for a station to transmit data stream; and        -   (ii) start and end period of prescheduled medium occupancy            period in which wireless medium occupancy is prescheduled,            and transmission is performed according to the prescheduled            wireless medium occupancy;    -   a controller unit which preschedules wireless medium occupancy        reservation having a duration period for contention successful        station in prescheduled medium occupancy period, and moves        forward the start period of contention medium occupancy period        of next selective contention period by the duration period;    -   a transmitter unit which transmits a beacon signal including        information for start period of the contention medium occupancy        period to the stations; and    -   a receiver unit which receives data stream transmitted from the        station.

The contention medium occupancy period and the prescheduled mediumoccupancy period are included in the selective contention period.

In the access point, when the receiver unit receives a null packettransmitted at the transmission timing according to prescheduledwireless medium occupancy reservation having a duration period for thestation, the prescheduled wireless medium occupancy reservation will becancelled, then start period of the contention medium occupancy periodof next selective contention period will be moved forward by theduration period.

The at least one station includes:

-   -   a receiver unit which receives the beacon signal including        information of the start period of the contention medium        occupancy period transmitted from the access point via the        wireless medium;    -   a transmitter unit which transmits data stream via the wireless        medium;    -   a medium recorder unit which records medium record; and    -   a controller unit which extracts the information of the start        period of the contention medium occupancy period from the beacon        signal, and monitors condition of wireless medium occupancy at        every monitoring period among the start period and the end        period of the contention medium occupancy period, then instructs        the transmitter to transmit data stream when the controller unit        confirms that wireless medium is not occupied.

In another station, when the station is successful for a contention atthe contention medium occupancy period of the selective contentionperiod, and acquires a wireless medium occupancy reservation having aduration period for the contention successful station, then the stationmay extract information of start period of the contention mediumoccupancy period of next selective contention period, and begins totransmit data stream at a time before the start period of the contentionmedium occupancy period by the duration period.

In a further station, the medium recorder unit may record the mediumrecord including condition of wireless medium occupancy in both thecontention medium occupancy period and the prescheduled medium occupancyperiod of the selective contention period, and the controller unit canalso calculate transmission timing at which the station transmits datastream in the prescheduled medium occupancy period according to thetransmission record.

In a still further aspect, when first and second stations areprescheduled respectively within the next prescheduled medium occupancyperiod, and the first station's transmitter unit transmits a null packetwhich is a kind of broadcasting packet sent to all stations in order torelease its own prescheduled wireless medium occupancy, and the secondstation's receiver unit receives the null packet from the first station,then the controller unit of the second station realizes that theprescheduled wireless medium occupancy reservation for the first stationis cancelled, and rearranges its transmission order of the secondstation within the next prescheduled medium occupancy period by usingthe medium record recorded by the medium recorder unit of the secondstation.

In the event, application data streams gain access to the wirelessmedium using contention based mechanism at the wireless medium controllayer, it is possible to selective choose the contention period for datastream this is admitted into the wireless network. Selective contentionfor all wireless station can begins after detecting the selectivecontention start indicator from the central controller of the wirelessnetwork. This indicator is broadcast periodically at the beginning ofthe selective contention period. The stations in the wireless networkcontrolled by the central controlled in a distributed manner updates thetransmission time of other stations as well as it's own. With thistransmission records, the stations can determine the optimal time tocontend for wireless medium and thereby reducing the contention timewithin the wireless network. The stations can reserve wireless medium bycontending using any contention methods in current selective contentionperiod and automatically reserve for the same medium occupancy time inthe next selective contention period. Deletion wireless mediumreservation is performed by simply not transmitting data packets atscheduled transmission time. All transmission and non-transmissionperiod at pre-scheduled time will be automatically updated in thetransmission records maintained by individual stations within thewireless network.

EFFECTS OF THE INVENTION

By applying the present invention, a network device is become more QoSaware. The number of transmission permit required serving QoS streamsare reduced. Contending of Wireless Medium is more scheduled and thusreducing the number of contention or collision as the wireless medium isshared by plural number of wireless station within a wireless networkadministered by a central controller. For a uninterrupted data streamtransmission, the present invention allow contention based wirelessmedium to reserve for bandwidth thereby reducing the number ofcontention for reserved bandwidth to zero. Zero contention provides aconstant transmission and reception behaviour at the transmitting andthe receiving station respectively. Having a zero or extreme smallcontention period, the bad characteristic of stream arrival behavioursuch as high jitter rate can be removed and allowing less complexinterface and software control mechanism implementation in the layerabove medium access controller.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will become readily understood from the followingdescription of preferred embodiments thereof made with reference to theaccompanying drawings, in which like parts are designated by likereference numeral, and in which:

FIG. 1 shows a High Level Message Sequence Chart for Wireless Stationsand Central Controller operating during a Selective Contention period;

FIG. 2 is a timing diagram of a typical Selective Contention Period;

FIG. 3 is a flowchart for updating Transmission Records;

FIG. 4 shows Central Controller in a Selective Contention Period;

FIG. 5 shows Operations of Transmission Record by Wireless Station;

FIG. 6 is a schematic view of the wireless network of the presentinvention;

FIG. 7A is a schematic view of the access point of the network;

FIG. 7B is a schematic view of the station of the network;

FIG. 8 is a flowchart for transmission via wireless medium acrosswireless network;

FIG. 9 is a flowchart for transmission via wireless medium acrosswireless network;

FIG. 10A is a conventional example of contention access mechanism withdata prioritization;

FIG. 10B is a schematic view of condition of wireless medium occupancyin station A and station B;

FIG. 11 is a schematic view of the beacon from access point;

FIG. 12 is a definition of Selective Contention Backoff Pointer;

FIG. 13A is a schematic view of selective contention between station Aand B;

FIG. 13B is a schematic view of condition of wireless medium occupancyin station A and station B;

FIG. 13C is a schematic view of beacon from the access point;

FIG. 14 is a schematic view of the data frame from the station;

FIG. 15A is a schematic view of selective contention between station Aand station B;

FIG. 15B is a schematic view of condition of wireless medium occupancyof station A and station B;

FIG. 16 is a schematic view of beacon from access point;

FIG. 17A is a schematic view of another aspect of selective contention;

FIG. 17B is a schematic view of the beacon from access point;

FIG. 18 is a schematic view of last data packet including nexttransmission information;

FIG. 19A is a schematic view of selective contention between station Aand station B;

FIG. 19B is a schematic view of condition of wireless medium occupancyof station A and station B;

FIG. 20 is a systematic process for Medium Dedication ScheduleGeneration; and

FIG. 21 is Finite State Machine for Transmission Permit Generator.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following description, for purposes of explanation, specificnumbers, times, structures, protocol names and other parameters are setforth in order to provide a thorough understanding of the presentinvention. The following paragraphs give an exemplification of how theinvention can be implemented. However, it will be apparent to anyoneskilled in the art that the present invention may be implemented withoutthese specific details. In other instances, well-known components andmodules are shown in block diagram in order not to obscure the presentinvention unnecessarily.

For a thorough understanding of the invention, here below, someoperation sequences, information data structures and techniques forcalculation are given. Certain data structures are used and they onlyserve as an example of the implementation of the present invention. Itis obvious to the person skilled in the art that in real implementation,new information could be added, and certain parts could be omitteddepending on the actual situation they are used in.

FIG. 1 gives an exemplification of selective contention, as disclosed inthis invention, to ensure subsequent zero contention period fortransmission of data packets belonging to a data stream after asuccessful reservation of medium occupancy based on contention method.For the purpose of a better description of this invention, FIG. 2 shouldbe used as a reference for a better understanding of the operations ofWireless Stations and Wireless Central Controller in a wireless networkwithin Selective Contention period.

FIG. 2 gives a description of the relationships of other sub-periodswithin one selection contention period, marked by literal (401).Selective Contention Period timing relationships depicted in FIG. 2would be a good reference when the embodiment related to FIGS. 2 and 3is read with the HMSC in FIG. 1.

Within one contention period, there are 2 sub-periods; (i) Pre-scheduledmedium occupancy (403) and (ii) Medium Occupancy Contention (404). ThePre-Scheduled medium occupancy period is used for data transmission forstations that have won the contention in (404) of previous SelectiveContention period. The pointer as indicated as SCB_Ptr, marked byliteral (405), is computed from the Selective_Contention_Backoff fieldof Selective_Contention_Information data structure. The Contentionback-offs adopted by each station could result in wireless mediumcontention, marked by literal (406), after all stations begin to contentfor data transmission rights. It is possible to have plural number ofcontentions (406) within the medium Occupancy Contention period.

With reference to seventh aspect of this invention, the high levelmessage sequence chart (HMSC) gives a typical life cycle of selectivecontention period occur within a wireless network where wirelessstations content for rights to transmit. The rights to content are madeknown to all stations by having a central controller broadcasting amessage containing timing parameters described in theSelective_Contention_Information structure, during the process marked byliteral (302). The information in the data structure,Selective_Contention_Information, provides an indication where thecontention for the 1st transmission of data stream can take place withinone selective contention period. Broadcasting of this message indicatesthe beginning of selective contention period or it can also be used toindicate the end of the selective contention period, based on the valuesof the Start_n_End parameter in the Selective_Contention_Information.This message is broadcasted at the beginning of the Selective ContentionPeriod and may be added at the end of the Selective Contention Periodand before the conditions marked by literal (301).

The message used to indicate the beginning of selective contentionperiod comprises of at least the following parameters:Selective_Contention_Information {   Start_n_End;/* A bit fieldindicating start or end of Selective Contention Period */  Selective_Contention_Backoff; /* a data field indicating length oftime the wireless stations, without prior medium occupancy grant, mustwait before contending can starts. Contention for bandwidth reservationis only allowable to the admitted data streams. This field is measuredin unit of time from the beginning of the broadcast ofSelective_Contention_Information message to the time where contention of1st medium occupancy request can take place */   Duration of SelectiveContention; /* duration of Selective Period */ }

It is possible to implement by appending all or part of theSelective_Contention_Information parameters in message format (1) toexisting data frames such as part of the beacon frame described in theIEEE802.11 specification disclosed in International Standard ISO/IEC8802-11: 1999: ANSI/IEEE Std 802.11, 1999 Edition—“Part 11: Wireless LANMedium Access Control (MAC) and (PHY) Specifications. Another way ofimplementing Selective Contention is to append all or part of theparameters of Selective_Contention_Information message in the form ofinformation element that could be transmitted by appending to theIEEE802.11 beacon frame. These beacon frame with theSelective_Contention_Information message that the information element isbroadcasted by the Medium Occupancy controller of the Wireless networkit governed periodically. Some of the parameters such as Duration ofSelective Contention can be implemented as a variable shared by allstations within the wireless network through SNMP's (Simple NetworkManagement Protocol) Management Information Based (MIB) value.

After receiving the message in (302), all stations in the wirelessnetwork are in the Pre-Alloted station Contention Active state, (303).All stations within the control of the wireless network shall onlytransmit data if there is prior wireless medium occupancy won as aresult of contention from previous selective contention period, (304).The precise time to transmit data packets from the data stream isprovided by the values stored in the Medium Occupancy vectors: Time fortransmission indicated by M_O_Vec[n] and transmission duration indicatedby M_O_Dur[n]. In the event, the station decides to cease datatransmission in the pre-Alloted Station Contention Active state, process(316), the station can choose to cease transmission or to send out aNULL data packet to indicate that the station has given up the MediumOccupancy time the station reserve in previous Selective Contentionperiod.

For Stations taking part in obtaining medium occupancy during thisselective contention period, transmitting stations must observe and keepa record of the m instances of Transmission silence period and mediumoccupancy period of a specified data stream admitted to the wirelessnetwork governed by a central medium occupancy controller. Theexemplification of this record described in this embodiment isTransmission Record {   M_O_Vec[n];/* Medium Occupancy Start timemeasured from the beginning of Selective_Contention_Information to thestart of Medium Occupancy time for stream n */  M_O_Dur[n]; /* MediumOccupancy Duration or End time */  S_Vec[m]; /* Transmission SilenceStart Time of instance m */  S_Dur[m]; /* Transmission Silence Durationor end time of instance m */ }

Stream Transmission time parameters is the time where the data packetsof the specified data stream are scheduled to contend for medium fortransmission. Transmission Silence time parameters are the time wherethe station should not content for the medium occupancy fortransmission. Transmission Silence vectors, consisting of S_Vec[n] andS_Dur[n], are contiguous transmission block separated only by timeperiods due to contentions or Medium Occupancy Vectors. Medium OccupancyVectors comprises of M_O_Vec[n] and M_O_Dur[n]. Transmission Silencetime are time observed by the stations not transmitting data at thespecified time from transmissions from other stations. In IEEE802.11,this value can be reflected in the Duration/ID field disclosed inInternational Standard ISO/IEC 8802-11: 1999: ANSI/IEEE Std 802.11, 1999Edition—“Part 11: Wireless LAN Medium Access Control (MAC) and (PHY)Specifications.

Transmission of data based on medium occupancy gathered from the StationTransmission record can take place in (304) if medium occupancycontention is successful by the station in the previous SelectiveContention period. Transmission data packets, in HMSC state marked byliteral (304) take place in (403) of the Selective Contention Periodtiming relationship depicted in FIG. 2. Based on theSelective_Contention_Backoff of the Selective_Contention_Information,all stations compute and keep a copy of SCB_Ptr (405) for the SelctiveContention Period and begin to content for 1st data transmission of thestream admitted to the wireless network. Contention for Medium Occupancyreservation, as shown in the HMSC in FIG. 1, can start by the station ifstation is in the condition marked by (305). Stations wishing to havethe 1st transmission of data packets from the admitted streams willbegins contending for Medium Occupancy as in (307).

Contentions and transmissions of data in a successfully contendedwireless medium occupancy period during the Medium Occupancy Contentionperiod as in (404) shall be allowed to be repeated in the Pre-ScheduledMedium Occupancy period in the next selective contention period (401).The station with a successfully contended medium occupancy in the periodas marked in (404) will be in the Contention Access Rights Grantedcondition (308) and allowed to transmit data packets, in processesmarked by literal (311) and (313). Process marked by (311) will beallowed to transmit up to (n-1) packets and process (313) transmit thenth packet, assuming there are n (where n>1) data packets fortransmission for the medium occupancy period granted from the successfulcontention. After transmitting (n-1) data packets, the transmittingstation of the medium occupancy period may choose to be in the statemarked by literal (312). In the (312) state, the station mayspecifically asked for similar amount of medium occupancy time in thenext selective contention period (401) by performing tasks in (314) and(315). In process marked by literal (314), station may choose toconsolidate the transmission of data packets of the data streamsadmitted won in the Medium Occupancy Contention Period, (404) for thenext transmission. Process (315) will make the necessary controlinformation to indicate that the wireless occupancy is needed to thecentral controller by appending the information in the last data packettransmission. The information sent in (315) is depicted theNext_Transmission data structure. Next Transmission {   Repeat_Flag;  /*A bit field to indicate to all stations and central controller that thenext Selective Contention Period should have the specified MediumOccupancy period or to have the Medium occupancy period release */  Stream Transmission Start;    /* time measured from the beginning ofSelective_Contention_Information transmission */   Stream TransmissionDuration or End time; /* End time of transmission of the data stream inunit time or measured from the beginning ofSelective_Contention_Information */ };

Both wireless central controller and wireless stations within thewireless network controlled by the said wireless central controller mustkeep a list of transmission by other stations during SelectiveContention Period by process marked by (310) during the UpdateTransmission Silence Period active condition (309). In the IEEE802.11,this is updates knows as the Network Allocation Vector disclosed inInternational Standard ISO/IEC 8802-11: 1999: ANSI/IEEE Std 802.11, 1999Edition—“Part 11: Wireless LAN Medium Access Control (MAC) and (PHY)Specifications updates.

On detecting the end of the Selective Contention Period, as detected inprocess (306), either it is through time out of the central timer orthrough the time out created by the station through the value in theDuration of Selective_Contention parameter of theSelective_Contention_Information, contention for wireless medium mustceased. The central controller would be in the process marked by (306),will then perform the updates based on the medium occupancy registeredin the Pre-Schedule Medium Occupancy Period and the Medium OccupancyContention Period, to create a new Selective_Contention_Backoffparameter for the next selective contention period. A new broadcastconsisting of the new Selective_Contention_Backoff parameter will bebroadcast to all wireless stations in the beginning of the SelectionContention Period.

FIG. 3 shows the detail depiction of the transmission silence andspecified stream transmission being updated at the station and thecentral controller that is responsible for broadcasting the data in theSelective_Contention_Information to the stations in the wireless networkthe central controller controlled in the Pre-Scheduled Medium OccupancyPeriod for the next Selective Contention Period. This is to eliminatethe contention time wasted in the Medium Occupancy Contention Period,(404), which will form part of the Pre-Scheduled Medium Occupancy Periodin the next Selective Contention period.

The implementation in FIG. 3 assumes that the Transmission Silencevector and Medium occupancy updates are based on inter-leavedtransmission silence and medium occupancy period. The update process inFIG. 3 can begins, (501), when the end of the Selective Contentionperiod. The central controller and the stations within the wirelessnetwork can use the same flowchart in FIG. 3 to create SelectiveContention Reservation Schedule within the Pre-Scheduled mediumOccupancy period for subsequent Selective Contention Period. SelectiveContention Reservation Schedule at the Stations consists of SilenceTransmission vector consisting of S_Vec[m] and S_Dur[m] parameters ofTransmission Record structure and Medium Occupancy vectors of stream nconsisting of M_O_Vec[n] and M_O_Dur[n] of the Transmission Recordsstructure. For each Selective Contention Reservation Schedule update,the total number of non-zero Silence Transmission vectors and MediumOccupancy Records kept by both station and central controller areupdated. Process block (503), determines the last point of TransmissionSilence of the last fragment and the Medium Occupancy vector nearest tothe consecutive Transmission Silence fragment or the next MediumOccupancy vector.

If next vector to be updated is a Transmission Silence fragment, the newTransmission Silence Fragment is updated based on the condition if thepreceding vector is a Medium Occupancy vector or Transmission SilenceVector. If current vector is a Medium Occupancy vector, process pathindicated in (504) will be selected. Medium Occupancy vector is updatedaccording to process in (506) and (509).

In the case of current vector is Transmission Silence Fragment, theupdates of Transmission Silence Fragment is updated according to (507),if the preceding vector is Medium Occupancy vector. Else if thepreceding vector is a Silence Transmission vector, the current vectorwill be updated and the duration of current vector will be added to thepreceding Silence Transmission Vector as in (508). The current vector isdestroyed as indicated in process (510) by initialising to null.

FIGS. 4 and 5 give an example of 3 stations contending selectively forthe wireless medium occupancy from the time the stream is admitted intothe wireless network to the time the deletion of stream. The timingdiagram illustrated in FIGS. 4 and 5 depicts the time the streams fromthe stations are admitted into and deleted from the network. Deletionand admission of streams are performed through additional signallingfrom upper layer network resource, (607). The time line indicated in(607), provides the time data stream are admitted into and exit from thewireless network. The scheduled broadcast of the Selective ContentionInformation by the central controller is shown in the timing chartindicated by literal (608). Contentions and the updates of the pointer(SCB_Ptr) derived from the value carries in the Selective ContentionBackoff parameters are also shown the timing chart.

Updates of the Transmission Record parameters are based on the valueused and indicated in the 4 Selective Contention Period, (613), (614),(615) and (616). The updates illustrated in the 4 Selective ContentionPeriod are performed at the end of the Selective Contention Period. Inthis illustration, the Selective Contention Period, (606), are boundedby two broadcast frames consisting of Selective_Contention_Information.

The timing line, marked by literal (609), illustrates the contention formedium occupancy in the Medium Occupancy Contention Period. Theresulting time chart, illustrated in time line (608), shows thecompaction time of Medium Occupancy periods resulted from thetransmission Silence and Re-Scheduled of Medium Occupancy updatesdictated by the process indicated by (501) of FIG. 3. All stations andcentral controller have to enforce how the transmission records areupdated. Time lines for Station A (610), Station B (611) and Station C(612) give the instances of Medium Occupancy contention being admitted,re-scheduled and deleted. At different Selective Contention Period, itillustrates the instances of the different parameters of transmissionrecords. In this example, deletion of Medium Occupancy by station A isbased on Option 1 of process (316) of FIG. 1.

For further illustrative purpose, time line (608) shows how terminationof Medium Occupancy can take place by having station A send out a nullpacket (604) in the Medium Occupancy granted in earlier SelectiveContention Period. This will allow the medium occupancy contention totake place among stations needing bandwidth on ad-hoc basis marked byliteral (605). The amount of time for contention and transmission ofdata is bounded by the previous medium occupancy given up by station A.

For a better understanding of the invention, here below, some operationexamples are given.

All the examples below will be described based on the scenario shown inFIG. 6. FIG. 6 is a schematic view of a wireless network including acentral controller (which can be called “Access point (AP)) and 3stations (A, B, C) available. Station A is trying to send audio data tothe AP and station B is trying to send video data to station C which isa kind of video display terminal. In conventional systems usingcontention access mechanism like CSMA/CA (carrier sense multiple accesswith collision avoidance), all stations who are senders like station A &B have to contend for channel access before every transmission.

FIG. 7A is a schematic view of the access point (10) of the wirelessnetwork. The access point (10) has a controller unit (12), a mediumrecorder unit (14), receiver unit (16), transmitter unit (18). Themedium recorder unit (14) records start and end period of contentionmedium occupancy period and start and end period of prescheduled mediumoccupancy period. Then, the stations (20, 30, 40) contend for wirelessmedium occupancy in order to transmit data stream in contention mediumoccupancy period. The wireless medium occupancy is prescheduled, andtransmission is performed according to the prescheduled wireless mediumoccupancy in prescheduled medium occupancy period. The contention mediumoccupancy period and the prescheduled medium occupancy period areincluded in the selective contention period. The controller unit (12)preschedules wireless medium occupancy reservation having a durationperiod for contention successful station in prescheduled mediumoccupancy period, and moves forward the start period of contentionmedium occupancy period of next selective contention period by theduration period. The transmitter unit (18) transmits a beacon signalincluding information for start period of the contention mediumoccupancy period to the stations. The receiver unit (16) receives datastream transmitted from the station (20).

FIG. 7B is a schematic view of the station (20) of the wireless network.The station (20) has a controller unit (22), a medium recorder unit(24), receiver unit (26), transmitter unit (28). The receiver unit (26)receives a beacon signal including information of start period ofcontention medium occupancy period transmitted from the access point(10) via the wireless medium. In the contention medium occupancy periodthe station (20) contends with other station for wireless mediumoccupancy to transmit data stream. The transmitter unit (28) transmitsdata stream via the wireless medium. The controller unit (22) extractsthe information of the start period of the contention medium occupancyperiod from the beacon signal, and monitors condition of wireless mediumoccupancy at every monitoring period among the start period and the endperiod of the contention medium occupancy period, then instructs thetransmitter to transmit data stream when the controller unit (22)confirms that wireless medium is not occupied.

FIG. 8 is a flowchart for transmission via wireless medium acrosswireless network. The transmission method includes:

(i) transmitting data stream from the station according to prescheduledwireless medium occupancy reservation for the station withinprescheduled medium occupancy period of a selective contention period(S01);

(ii) performing a contention between the stations for wireless mediumoccupancy for a contention successful station to transmit data streamwithin only contention medium occupancy period of the contentionselective period (S02);

(iii) transmitting data stream from the contention successful stationafter the contention (S03); and

(iv) prescheduling a wireless medium occupancy reservation for thecontention successful station to transmit within a prescheduled mediumoccupancy period of next selective contention period (S04).

FIG. 9 is a flowchart for another transmission via wireless mediumacross wireless network. The transmission method includes:

(i) transmitting a beacon signal including an information about startperiod of the contention medium occupancy period to each station (S11);

(ii) transmitting data stream from the station according to prescheduledwireless medium occupancy reservation for the station withinprescheduled medium occupancy period of a selective contention period(S12);

(iii) performing a contention between the stations for wireless mediumoccupancy for a contention successful station to transmit data streamwithin only contention medium occupancy period of the contentionselective period (S13);

(iv) transmitting data stream from the contention successful stationafter the contention (S14); and

(v) prescheduling a wireless medium occupancy reservation for thecontention successful station to transmit within a prescheduled mediumoccupancy period of next selective contention period (S15);

(vi) moving forward start period of a contention medium occupancy periodof next selective contention period by the duration period (S16).

FIGS. 10A, 10B, and 11 shows a conventional example of contention accessmechanism with data prioritization. At the beginning of each contentionperiod (701,702,703), AP periodically broadcasts a frame called “beaconframe” (704,707,712) in order not only to perform timing synchronizationbut also to indicate broadcasting information to all stations associatedwith itself. After receives the beacon frame, all the senders (station A& B) start contending for channel access.

As shown in FIGS. 10A and 10B, station A performs carrier sense in the1st period (701) and because the carrier sense indicates that channel isidle (nobody's using the channel) station A performs its transmission(706) immediately after the carrier sense. Then, station A is successfulfor the contention (705) in the 1st period (701). After station A endsup its transmission (706) in the 1st period (701), it has to wait for arandom period before performing the next carrier sense. Basically, therandom period of time that a station has to wait before performing itsnext carrier sense is called “Random Backoff time” and the operation towait for a Random Backoff time is called “perform (random) backoff”.After the transmission (706) in the 1st period (701), station A performsrandom backoff and then perform carrier sense again in the 2nd period(702). However, the carrier sense indicates that channel is busy(because the channel is occupied by station B) so station A has toperform random backoff again immediately after the carrier sense. Then,station B is successful for the contention (708) in the 2nd period(701).

All the operations as described in the above paragraph are beingperformed and repeated by each sender station. This kind of accessmechanism allows for automatic channel sharing and reduce the collisionprobability which rapidly increases with an increase of sender stations.

In addition to the access mechanism, data prioritization can also beintroduced to provide a suitable QoS for different data type asdescribed in FIG. 11. For example, AP can determine “Maximum backofftime” for each Data type in order to control average random backoff timeto meet different delay bound conditions required by each data type.Here, “Maximum backoff time” indicates a maximum value that limit theupper bound of random backoff time. For example, if “Maximum backofftime”=0.1 ms, this means that random backoff time must be a random valuewhich is more than 0 ms but less than 0.1 ms.

Suppose that data type is divided into 3 types, Audio, Video, and Text.Basically, Audio data type requires the most severe delay boundcondition (shortest delay bound) compared to the other data types soMaximum random backoff time for Audio should be smaller than Video andText type. In the case of Video data type, Video data also requires asevere delay bound condition but not as much as Audio data so Maximumrandom backoff time for Video should be larger than Audio type butsmaller than Text type. According to the above consideration, AP cancontrol average random backoff time for each data type by indicating a“Table of contention parameters” in beacon frame like shown in FIG. 11.Parameters indicated inside the table can be adjusted according to loadconditions, channel conditions, etc. to provide a suitable QoS for eachdata type. In case of FIG. 11, we can see that because “Maximum backofftime” for Audio data is set to be smaller than that for Video data,station A who is sending Audio data tends to have more chances to accessthe channel than station B. According to this, average packet delay forAudio data transmitted by station A can be expected to be shorter thanthat for Video data transmitted by station B.

However, under high contention conditions, for example when traffic loadis high or when a number of users is large, because a probability thatcarrier sense will indicate idle is very low, the probability that QoSconditions such as delay bound etc. required by a station can not besatisfied is very high even for station A who has the highest accesspriority (shortest Maximum backoff time). In other words, it is hard toprovide QoS guarantee by a contention based access mechanism in which asender has to perform contention (carrier sense with random backoff)every time before transmission. In order to cope with this problem, theinvention access mechanism which is called “Selective Contention” isproposed.

FIGS. 12 to 19 show concepts of the invention access mechanism“Selective Contention”.

FIG. 12A shows a definition of Selective Contention Backoff Pointer. Inorder to perform selective contention, a new information called“Selective_Contention_Backoff” is introduced by indicating it in thebeacon frame as shown in FIG. 12A. This information is also beingdemonstrated as SCB_Ptr (1) in the transmission sequence as shown at thetop of the same figure.

The “selective contention period” (2) indicates duration of selectivecontention period. This information acts as same as the contentionperiod as shown in FIG. 10A.

At the initial stage (1st period) (61), AP indicates“Selective_Contention_Backoff”=0 which means that the whole SelectiveContention Period is recognized as “Contention Medium Occupancy Period”.In this case, a conventional contention access as explained in FIGS. 10Aand 10B can be performed immediately after the beacon (65,68,72,75).

In this 1st period, station A contends for channel access and occupieschannel for 2 ms. Then, station A is successful for the contention (66)in the “Contention Medium Occupancy Period” (61). Suppose that station Ahas more data to transmit, AP registers station A as “Pre-scheduledstation” to allow station A to repeat its transmission from the nextselective contention period (2nd period). According to the registration,AP has to indicate to all stations that a period of 2 ms after thebeacon of the 2nd period is “Pre-Scheduled Medium Occupancy period” (62)and is reserved for a “Pre-Scheduled station(s)” which in this case isstation A. AP broadcasts such information to all stations by indicating“Selective_Contention_Backoff”=2 ms in the beacon of the 2nd period asshown in the FIG. 10B. According to this, only station A can gain accessto the channel for 2 ms during “Pre-Scheduled Medium Occupancy period”of the 2nd period without performing any contention. After the“Pre-Scheduled Medium Occupancy period” (62), the remaining time untilthe next beacon (72) will be transmitted is automatically recognized byall stations as “Contention Medium Occupancy Period” (63).

Consequently, all stations which is not being registered as“Pre-Scheduled station” has a right to contend for a channel access inthis “Contention Medium Occupancy Period” (63).

As shown in FIGS. 12A and 12B, we can see that in the 2nd period afterthe end of “Pre-Scheduled Medium Occupancy period” (62), station Bstarts contending for channel access (71) and occupies channel for 3 ms.Then, station B is successful for the contention (70) in the “ContentionMedium Occupancy Period” (63). Suppose that station B has more data totransmit, AP also registers station B as “Pre-scheduled station” toallow station B to repeat its transmission from the next selectivecontention period (3rd period). According to the registration, AP has toindicate to all stations that a period of 5 ms after the beacon (72) ofthe 3rd period is “Pre-Scheduled Medium Occupancy period” (64) and isreserved for a “Pre-Scheduled station(s)” which in this case are stationA & B. AP broadcasts such information to all stations by indicating“Selective_Contention_Backoff”=5 ms in the beacon (72) of the 3rd periodas shown in the FIG. 12A. According to this, both station A and stationB can gain access to the channel (73,74) for 2 ms and 3 ms respectivelyduring “Pre-Scheduled Medium Occupancy period” (64) of the 3rd periodwithout performing any contention.

The invention selective contention allows any station which succeeds itsfirst contention access once and is registered by the AP as“Pre-scheduled station” to gain access to the channel periodicallywithout contention. It is clear that the invention can drasticallydecrease contention and also provide a better QoS guarantee than theconventional contention mechanism even when traffic load is high or whena number of users is large.

Next, let's focus on the transmission record which is also introduced inthe invention in addition to the Selective_Contention_Information. Thereason that each station has to keep transmission record individually isdescribed below based on the situation shown in FIGS. 13A, 13B, 13C, and14. In FIG. 13A, both station A and station B contend for channel accessand occupy the channel for 2 ms and 3 ms respectively in the 1st period(61). Then, station A is successful for the contention (82) and stationB is successful for the contention (84) in the “Selective ContentionPeriod” (61). AP registered both station A and station B as“Pre-scheduled stations” and indicates “Selective_Contention_Backoff”=5ms in the beacon (86) of the 2nd period to reserve a time period of 5 msafter the beacon for station A and B. After received the beacon (86) ofthe 2nd period, station A and B checks their own transmission recordobserved in the 1st period (61). By checking the transmission record ofthe previous Selective Contention Period, each “Pre-scheduled station”can confirm its

1. transmission order and

2. time to start and end transmission in the current SelectiveContention Period.

As shown in the FIG. 13A, station A can confirm that in the 1st period(61) it won a contention at the 1st order and occupied channel for 2 ms.Station A can also confirm that after its transmission (83) the channelwas occupied (85) by someone (station B in this case) for 3 ms.According to this, station A can decide that it must performtransmission at the 1st order again in the 2nd period. Consequently,station A starts its transmission (87) without contention immediatelyafter the beacon (86) in the 2nd period.

As for station B, station B can confirm that in the 1st period (61) itwon a contention at the 2nd order and occupied channel (85) for 3 ms.Station B can also confirm that before its transmission (85) the channelwas occupied (83) by someone (station A in this case) for 2 ms.According to this, station B can decide that it must performtransmission at the 2nd order after waiting for 2 ms in the 2nd period.Consequently, after received the beacon (86) of the 2nd period station Bwaits for 2 ms and then starts its transmission (88) without contention.Station B occupies the channel for 3 ms until the end of “Pre-ScheduledMedium Occupancy period” (62) of the 2nd period. The operations occurredin the 2nd period as described above are being repeated on and on everyselective contention period.

“Silence” in the transmission record as shown in FIG. 13B is the timeperiod where other stations are performing their transmission and thestation has to keep silence (not transmitting anything) in order not tointerfere transmission of other stations. In IEEE802.11 systems, astation can decide when it should be silence by observing theDuration/ID field indicated in the frames sent by other stations. TheDuration/ID field is indicated as “Network Allocation Vector (NAV)field” as shown in FIG. 13B. This field is basically indicated in theframe header of each frame.

The details of how to update transmission record parameters can bereferred to FIGS. 3 to 5.

It is clear that an introduction of transmission record helps“Pre-Scheduled stations” to decide its transmission order and starttime. However, if any station has a mistake in its transmission record,the station may perform transmission with wrong order, which leads to anoccurrence of collision inside “Pre-scheduled Medium Occupancy Period”.To avoid such problems, “Pre-scheduled Station Address List” as shown inFIG. 15A can also be introduced in addition to the “transmission record”

“Pre-scheduled Station Address List” is indicated in a beacon frame andused to tell all stations that

(1) Which stations are currently registered as Pre-scheduled stations?

(2) What is the transmission order for each Pre-scheduled station?

(3) How long can a Pre-scheduled station occupy the channel in“Pre-scheduled Medium Occupancy Period”

(1) is indicated as “Pre-scheduled Station Address”, (2) is indicated as“Order” and (3) is indicated as “Stream Transmission Duration” in theFIG. 16.

AP indicates “Pre-scheduled Station Address List” within every beaconframe and broadcasts to all stations at the beginning of every SelectiveContention Period.

FIG. 17A, 17B, and 18 shows how to use Next Transmission Information. Asexplained above, the station which successfully contended channeloccupancy in “Medium Occupancy Contention Period” will be allowed totransmit data packets without contention in “Pre-scheduled MediumOccupancy Period” from the next Selective Contention Period. A stationcan indicates its intention whether to continue transmission in the nextSelective Contention Period or to suspend transmission and release itsown Pre-scheduled medium occupancy time, by indicating Next transmissionInformation in the last packet transmitted in the current SelectiveContention Period.

In the FIGS. 17A, 17B, and 18, station A indicates “Repeat-Flag”=ON with“Stream_Transmission_Duration”=2 ms in the Next Transmission Informationfield of the last packet transmitted in the 1st period in order continueits transmission in the 2nd period. According to this, AP registersstation A as “Pre-scheduled station” and reserves a time period of 2 msby indicating “Selective_Contention_Backoff”=2 ms in the beacon frame ofthe 2nd period. After receives the beacon, station A occupies thechannel for 2 ms by continuously transmitting data packets withoutcontention in the 2nd period. Here, suppose that station A wants tocontinue its transmission in the 3rd period with transmission durationof 4 ms. In this case, station A indicates “Repeat_Flag”=ON again butchange the value of “Stream_Transmission_Duration” to 4 ms in the NextTransmission Information field of the last packet transmitted in the 2ndperiod in order continue its transmission in the 3rd period. Accordingto this, AP reserves a time period of 4 ms by indicating“Selective_Contention_Backoff”=4 ms in the beacon frame of the 3rdperiod. After receives the beacon, station A occupies the channel for 4ms by continuously transmitting data packets without contention in the3rd period. Here, suppose that station A wants to stop transmission fromthe next (the 4th period) Selective Contention Period. In this case,station A indicates “Repeat_Flag”=OFF in the Next TransmissionInformation field of the last packet transmitted in the 3rd period inorder to release the Pre-scheduled medium occupancy time of 4 msreserved for itself. According to this, AP indicates“Selective_Contention_Backoff”=0 ms in the beacon frame of the 4thperiod. Consequently, at the 4th period, the whole selective contentionperiod is recognized as “Contention Medium Occupancy Period” as shown inthe FIG. 17B.

A Pre-scheduled station can also release its own Pre-scheduled mediumoccupancy time by sending a broadcasting frame such as “Null Frame” toAP and all stations whenever it wants as shown in FIGS. 19A and 19B.FIGS. 19A and 19B show an example for suspension of Pre-scheduledtransmission by using Null Frame. As shown in the FIGS. 19A and 19B,station A which is a “Pre-scheduled station” sends Null frame in the 2ndperiod to indicate that it wants to suspend its transmission in“Pre-scheduled Medium Occupancy Period”. Upon reception of Null Frame,AP and other Pre-scheduled stations recognize that transmission order inthe “Pre-scheduled Medium Occupancy Period” changes and have to beupdated. In this case, station B which is “Pre-scheduled station”confirms its own transmission record and finds that station A which wasa “Pre-scheduled station” transmitting at the first order has alreadysuspended its “Pre-scheduled transmission”. Consequently, allPre-scheduled stations except station A recognize that they have toperform “Pre-scheduled transmission” at 1 step younger order. In thiscase, station B which previously performed “Pre-scheduled transmission”at the second order recognize that it transmission order is changed fromthe second (2nd) order to the first (1st) order. And at the same time,AP release Pre-scheduled medium occupancy time of 2 ms which is reservedfor station A by updating the value of “Selective_Contention_Backoff”from 5 ms to 3 ms and indicating “Selective_Contention_Backoff”=3 ms inthe beacon of the 3rd period.

According to this, after receives the beacon of the 3rd period, stationB starts its Pre-scheduled transmission immediately as shown in theFIGS. 19A and 19B.

The invention solves the problems by providing a systematic process toequip the network device to become QoS awareness; a means to rejectadmission of stream that will cost transmission medium to be overloaded;a means to shape the emission rate of data units in a form of shortburst in order to reduce the number of transmission permit required; ameans to generate transmission permit to serve multiple transmissionqueues concurrently; a means to transmit data units of all the trafficstreams in the manner that QoS requirement is not being violated; ameans of creating a bounded period called the selective contentionperiod for controlled contention of wireless medium occupancy time; asystem where the stations and the central controller contend forwireless medium at a selected time in every selective contention perioddepending on the traffic conditions; a means for the stations andcentral controller to have a distributed scheduling of transmission bykeeping a transmission records at each stations; a means to update thetransmission records; a means to reserve and delete scheduled mediumoccupancy time within the selective contention period. a system toreserve and delete schedule medium occupancy time using contention basedwireless medium occupancy access method.

OPERATION OF THE INVENTION

With the present invention, all traffic streams with transmission beingcoordinated are being rate controlled and shaped before emitting into asingle transmission queue. Data units of all traffic streams in thetransmission queue are being served in First-In-First-Out fashion. Onthe other hand, for traffic streams with transmission not beingcoordinated are being admission controlled and categorized beforeemitting to their respective category transmission queue. Data units ina transmission queue are only permitted for transmission whentransmission permit for that queue is granted. Furthermore, theirrespective Transmission Controller of a transmission queue iscoordinating the transmission process.

In order to rapidly adapt to the transmission conditions of a wirelessmedium, Quality of Service (QoS) support should be enabled at the lowestpossible layer of the 7-layer OSI reference model. FIG. 20 shows asystematic process to facilitate QoS for transmission over a wirelessnetwork. Initially the traffic stream needs to be classified accordingto the manner in which it needs to be served, as marked by literal 101.The time at which data transfer is initiated can either beingcoordinated by a centralized coordinating entity or determined by anautonomous means. Parameterised or prioritised QoS streams can be servedby either: coordinated transfer, or autonomous transfer, depending onthe choice of the network device or setup.

For traffic streams that are to be served in the coordinated manner, theemission of traffic is to be rate controlled (103) and shaped (104)individually, before being admitted to the transmission queue. By doingso, data units can be transmitted in First-In-First-Out (FIFO)mannerwithout introducing a bias towards any traffic stream. Furthermore, itfacilitates data transmission without the need for making a decision onthe data unit to be transmitted when a transmission permit is granted.This process is especially useful when the transmission permit isdedicated to a network device, without specifically indicating anytraffic stream. The Traffic Shaper shapes the quantity (measured interms of either: a) the number, or b) the size) of data units that arepermitted to be admitted to the corresponding transmission queue. Thefirst process for Traffic Shaping (104) is to determine a serviceinterval for each transmission queue. The service interval is defined asthe duration between successive dedications of transmission-permits thatis required by a transmission queue in order to achieve QoS requirementsfor all admitted streams. In order to compute the service interval,first determine the quantity of data units, S, that are to betransmitted from the queue within a specific interval, I. Then computethe duration, D, that is required on the transmission medium to fullytransmit one data unit considering all the overheads. Then compute thetotal duration required to transmit all the data units that are to betransmitted during 1, represented as T, where: T=S*D. Using the value T,above, compute the minimum number of transmission permits required, P.Finally, the result obtained from the division of I by P is the value ofthe service interval. After determining the service interval, the valuesof: a) Service_Credit, b) Service_Negative_Credit and c) Service_Countneed to be computed.

Service_Credit is defined as the average quantity (measured in terms ofnumber or size) of data units that can be admitted to the transmissionqueue within a Service Interval. This is computed as the product of theservice interval with the sum of the data rates for all admitted trafficstreams. Service_Negative_Credit is defined as the surplus quantity ofdata units that can be admitted to the transmission queue, within aservice interval. It is used to smooth the traffic that is generated atburst without introducing excessive queuing delay. The third variable,Service_Count is the accumulated number or size of data units of thetraffic stream that are permitted to be transmitted but have not beingdo so from the beginning of the stream transmission. It is beinginitialised to zero before any data units is emitted into thetransmission queue. At the beginning of each periodicity of serviceinterval, Service_Credit is added onto the existing value of thevariable. After each transmission, a unit is being subtracted from thevariable.

At the periodicity of service interval, the quantity of data units, Nthat are permitted to admit into the transmission queue during thecurrent periodic interval is to be determined. If the value ofService_Count at the end of pervious periodic interval is greater thanzero, then N is equal to the sum of Service_Count, Service_Credit andService_Negative_Credit. Else, N is equal to the sum of Service_Count,Service_Credit only. Then this number is used to guard the emission ofdata units into transmission queue.

Finally, Transmission Controller (108) is to convert transmission permitto control signal (107) for controlling data transmission, which is alsogenerates necessary signals or control frames to release excessivetransmission permit base on transmission queue status (106).

For the traffic streams that determine their transmission timeautonomously, each stream needs to be admitted by the admission controlunit (112). The admission control unit determines whether admission ofthe stream will require more resources than are available in the networkand based on this calculation, it will decide whether to accept orreject the stream. The admission control unit (112) requires two inputs,namely: a) the estimated data rate of the traffic stream, and b)bandwidth available in the medium prior to admitting the stream. Thedata rate of a traffic stream can be estimated by monitoring the numberof data units and their size at the input terminal of the Trafficprioritiser (114). A station can estimate the bandwidth available in themedium by monitoring it own transmission and the setting of its NetworkAllocation Vector (NAV). Furthermore, the emission rate is to be mouldin a form of short burst in order to reduce the occurrences ofcontending for transmission permits with other streams or stream ofother network devices in the same transmission network. For TrafficShaper marked by literal 116, it is having the same functionality asdescribe for the traffic shaper marked by literal 104 with a minormodification on the method to determined the required service interval.The service interval is to be determined as a interval of transmissionpermit dedication that is able to maintain QoS Requirement of allstreams in the respective transmission queue. First is to obtain theduration of transmission permitted, E, when given a transmission permit.Then, compute the quantity of data units, F that can be transmitted induration E. The service interval is the division result of F over therate that data units are emitted to the transmission queue.

Transmission Controller (118) is to control the transmission of thepacket at the transmission queue and generate necessary signal to theTransmission Permit Generator to request for transmission permit.Request_To_Transmit signal (120) is being generated to the TransmissionPermit Generator when the respective transmission queue is non-empty andno pending signal request is being generated. Transmit Permit Generatorlogic can be represented by a two stages Finite State Machine as shownin FIG. 21 with three variables associated with each transmission queue.The first variable, A is to indicate the remaining number of fixed slotthat the transmission medium need to remain silent before a transmissionpermit can be granted to the transmission queue. The second variable, Wis to indicate that the transmission queue is having a pending requestfor transmission permit. It is set to true when Request_To_Transmitsignal (205) is being received and set to false when Clear_To_Transmitsignal (206) is generated. In the IDLE stage (201), at each slotinterval, A is being decremented by 1 if it is non-zero. Furthermore,when A is zero and W indicating there is a pending Request_To_Transmitsignal for the respective transmission queue, Clear_To_Transmit signalis to be generated. A transition from IDLE stage to BUSY stage isrequired when the transmission medium is detected to be busy. In BUSYstage (202), A is stop from decrementing. When the transmission mediumis idle for a pre-fix duration, a stage transition from BUSY to IDLE isto be performed. During that transition, A is to be recomputed. Withthat, only a single Transmission Permit Generator is required to servemore than one transmission queue.

The invention can have the following structures viewed from variousaspects. According to the first, a system that enables a network deviceto facilitate QoS data transmission in which the timing to initiatetransmission by the device is coordinated, comprising of:

i) A rate controller to police the emission of traffic stream into thetransmission queue such that it does not overuse the dedicated bandwidthand violates the pre-negotiated transmission rate.

ii) A Traffic Shaper to mould the emission rates of all traffic streamsinto a transmission queue, such that it can be served inFirst-In-First-Out fashion without introducing bias towards any stream.

iii) A Transmission Controller to generate the necessary signals tocontrol the transmission of a packet at the transmission queue and torelease a transmission permit.

According to the second, a system that enables a network device tofacilitate QoS data transmission, in which the timing to initiatetransmission by the device is determined autonomously by the device,comprising of:

i) An Admission Controller to grant transmission permission to a newlyinitiated traffic stream such that transmission channel is notoverloaded by the admission of the new stream.

ii) A Transmission Controller to generate the necessary signals torequest for transmission permits and to control the transmission of thepacket at the transmission queue.

iii) A Transmission Permit Generator to generate a transmission permitfor a device to initiate transmission.

According to the third, a method to ensure no bias is introduced bycombining all the data units of all traffic streams that are to betransmitted in a coordinated manner at the transmission queue, in orderto allow data units to be transmitted in a timely and First-In-First-Outfashion, when granted a transmission permit, comprising the steps of:

i) Performing rate control to police the emission rate of a trafficstream into the transmission queue such that it does not violate thepre-negotiated rate.

ii) Performing traffic shaping to mould all the emission rates of thetraffic streams into a transmission queue such that it can be served inFirst-In-First-Out fashion without introducing unfairness to any stream.

According to the fourth, method to achieve traffic shaping in part (ii)of above third aspect comprising the steps of:

i) Determination of a periodicity interval for the operation.

ii) Computation of the average number, or size of the data units thatare to be transmitted in duration of the periodic interval in order tosatisfy the QoS requirements of the traffic stream.

iii) Compute the variation of the average number, or size of the extradata units that are permitted to be transmitted during the periodicinterval duration, in order to satisfy the QoS requirements of thetraffic stream that are not generated at a constant bit rate calculatedover the periodic interval.

iv) Compute the accumulated number, or size of data units of the trafficstream that have been permitted, but not yet transmitted, from thebeginning of the stream transmission. This value is obtained by addingthe value as computed in part (ii) at the beginning of each periodicinterval, while subtracting a unit for each transmission that is made.

v) Determine the number or size of data units of the traffic stream thatare permitted to enter the transmission queue during the currentperiodic interval. This value is determined at the beginning of eachperiodic interval by adding the value computed in part (ii) to the valueof obtained in part (iv) at the end of previous periodic interval if thevalue is not greater than zero. Otherwise the values computed in parts(ii) and (iii) are added to the value obtained in part (iv) at the endof previous periodic interval.

According to the fifth, method to determine the periodicity interval inpart (i) of fourth aspect, when the transmission permit given to atransmission queue has a constant duration comprises the step of:

i) Compute the number or size of data units can be transmitted in theconstant duration.

ii) Compute the duration required for the transmission queue to befilled with the number or size of data units computed in part i.

According to the sixth, method to have only one Traffic Permit Generatorfor multiple transmission queues is to implement the generator processas two stages finite stage machine that comprises of:

i) A variable associated to a transmission queue indicating theremaining number of fixed slot that the transmission medium need to beremains silent before a transmission permit can be granted to thetransmission queue.

ii) A variable associated to a transmission queue indicating that thetransmission queue is having a pending request for transmission permit.

iii) An IDLE stage to decrement the variable in part i if it is non-zeroat each slot interval and grant transmission permit when a transmissionqueue is having pending request for transmission permit and therespective variable in part i is zero. A transition from IDLE stage toBUSY stage is performed when granting transmission permit is notallowed.

iv) A BUSY stage that is to stop decrement the variable in part i ateach slot interval. A transition from BUSY to IDLE stage is performedwhen the transmission medium has been IDLE for prefix duration.

According to the seventh, method for of reducing wireless mediumoccupancy contention where the wireless stations content fortransmission bandwidth by dividing into 2 distinct periods of wirelessmedium occupancy contention, the 2 distinct periods are:

i) Pre-Scheduled medium occupancy period where transmission withcontention and transmission without contending is allowable to wirelessstation that has previously gain medium occupancy period throughsuccessful contention in the wireless medium occupancy contentionperiod; and

ii) Medium occupancy contention period where wireless stations cancontend for wireless medium occupancy.

According to the eighth, method to bound selective contention period, inseventh aspect, by allowing a central controller of the wireless networkwhere wireless stations perform selective contention by broadcasting adata message with the following parameter:

i) A bit field indicating start and end of the selective contentionperiod;

ii) A numerical representation indicating the time wireless stations canbegin contending and reserve for medium occupancy period in current andnext selective contention period; and

iii) A numerical representation indicating the durations of theselective contention period.

According to the ninth, method for all stations to generate theselective contention period, as in seventh aspect, within the wirelessnetwork controlled or coordinated by a central controller on receptionof a signal or message indicating the beginning of the selectivecontention period and by retrieving the following pre-stored numericalrepresentatives from the message consisting of:

i) A representative indicating the time wireless stations can begincontending and reserve for medium occupancy period in current and nextselective contention period; and

ii) A representative indicating the durations of the selectivecontention period.

According to tenth, method to signal contention based medium occupancyreservation within the wireless network using a numerical representedcounter or pointer to indicate the beginning of contention time andduration within a bounded period where the bounded period is describedin seventh aspect, to control contention for medium occupancyreservation.

According to eleventh, method to prevent wireless medium contentionduring a period occupied by wireless medium occupancies belonging toother stations through successful contention based reservations byhaving a transmission records of a bounded period of time where thetransmission records are managed by individual station within thewireless network and the records comprises of:

i) Medium Occupancy Start time of all data streams of the host wirelessstation;

ii) Medium Duration of all corresponding data streams of the hostwireless station;

iii) The start time of a continuous period of wireless medium occupancyof other wireless stations observed by the host wireless station; and

iv) Durations of a continuous period of wireless medium occupancy ofother wireless stations observed by the host wireless station.

According to twelfth, a system for reserving bandwidth in a wirelessnetwork where medium occupancies generated by transmitting stationsusing contention means by allowing transmission records, as in eleventhaspect, to be updated in a distributed manner comprises of mediumoccupancies periods of data streams to be transmitted by the hoststation and transmission silence period observed by the host stationsdue to medium occupancy period allotted to other stations.

According to thirteenth, method to reduce bandwidth wastage due tocontention of wireless medium occupancy reservations in the mediumoccupancy contention period by freeing up the bandwidth for contentioncomprises the steps of:

i) Appending new blocks of transmission silence period separated only bycontention time to form a larger transmission silence period; and

ii) Removing contention time of Medium Occupancy Period betweentransmission silence periods or another Medium Occupancy Period.

According to fourteenth, method to reserve medium occupancy period fornext selective contention period without transmitting bandwidthreservation in subsequent selective contention period by sending mediumoccupancy reservation parameters in the last data packet in currentmedium occupancy period where the bandwidth reservation parametersconsists of:

i) Repeat Flag to indicate that the reservation of wireless mediumoccupancy time as specified in following part (ii) and (iii) to beremoved or added in the next bounded period;

ii) A time to indicate the transmission start time measured in referenceto the beginning of the bounded period; and

iii) A representative to mark the duration of medium occupancy time asin above part (ii).

According to fifteenth, method to remove reserved medium occupancy timein the pre-scheduled medium occupancy period by not transmitting in thereserved medium occupancy period and allowing the other wireless stationto content for transmission by using the updates of transmission recordsof stations in the wireless network.

According to sixteenth, method to remove reserved medium occupancy inthe pre-scheduled medium occupancy period by transmitting a null packetto signal to other stations to content for medium occupancy within thepre-scheduled medium occupancy time.

According to seventeenth, a system allowing other stations in thewireless network to content for medium occupancy time released by thestation by performing individual station transmission record updatesfrom the received null packet from the station releasing mediumoccupancy.

According to eighteenth, method to mould the emission of data units in ashort burst in order to reduce the occurrences of collision with otherstreams or streams from other network devices in a same network thattransmission are not being coordinated by a coordinator comprises thesteps of:

i) Performing traffic shaping for the data emission to transmissionqueue; and

ii) Requesting Transmission Controller to generate a signal to requestfor transmission permit.

According to nineteenth, method to determine the timing for theTransmission Controller of part iii in second aspect or of part ii ineighteenth aspect to generate a signal to request for transmissionpermit which is less likely to collide with other transmission comprisesby monitoring the status of transmission queue such that the signal torequest for transmission permit is only generated if there are enoughdata units to be transmitted upon receiving transmission permit with thecondition that the delay of the signal generation does not cost thelifetime of any data units to be expired.

According to twentieth, method for the stations to content for mediumoccupancy medium within the bounds of a selective contention period, asmentioned in seventh aspect, using a distributed and self regulatedcontrol states where the controls states comprises of:

i) Beginning of Selective Contention period state where the centralcontroller send a message comprises of parameters illustrated in eighthaspect and the other stations wait for the successful reception of thesaid message;

ii) Pre-Allotted Station Contention state where stations with priorsuccessful contentions in preceding selective contention period contendare allowed to content at specific time based on transmission record, asin eleventh aspect, for wireless medium occupancy time;

iii) Contention Reservations state is a state where stations can contendand reserve for medium occupancy in current and next selectivecontention period respectively. Stations participating in the selectivecontention period will also update the contention schedule for mediumoccupancy time of successful medium occupancy time period executed byother stations in this state;

iv) Stations with a successful contention will be in the contentionaccess rights granted state where data packets of a data stream aretransmitted;

v) Stations may traversed through the Advance Contention AvoidanceActive state, within the state described in above part (iv) if saidtransmitting station choose to reserve medium occupancy in the nextselective contention period; and

vi) After transmitting all data packets reserved for the mediumoccupancy time in the successful contention as in above part (iv), thetransmission record of the station is updated in the Update TransmissionSilence Period Active state.

Although the present invention has been described in connection with thepreferred embodiments thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications areapparent to those skilled in the art. Such changes and modifications areto be understood as included within the scope of the present inventionas defined by the appended claims, unless they depart therefrom.

1. Method for transmitting data stream via wireless medium forcontention based medium access across a wireless network having aplurality of stations and an access point communicating to said stationsvia wireless medium, the method comprising: (i) performing a contentionbetween the stations for wireless medium occupancy for a station totransmit data stream at a selective contention period; (ii) transmittingdata stream from the contention successful station after the contention,wherein the selective contention period is divided into two distinctperiod as: (a) contention medium occupancy period at which the stationscontend for wireless medium occupancy for a station to transmit datastream; and (b) prescheduled medium occupancy period at which a wirelessmedium occupancy reservation for a contention successful station isprescheduled.
 2. Method for transmitting data stream via wireless mediumfor contention based medium access across a wireless network having aplurality of stations and an access point communicating to said stationsvia wireless medium, the method comprising: (i) transmitting data streamfrom the station according to prescheduled wireless medium occupancyreservation for the station within prescheduled medium occupancy periodof a selective contention period; (ii) performing a contention betweenthe stations for wireless medium occupancy for a contention successfulstation to transmit data stream within only contention medium occupancyperiod of the contention selective period; (iii) transmitting datastream from the contention successful station after the contention; and(iv) prescheduling a wireless medium occupancy reservation for thecontention successful station to transmit within a prescheduled mediumoccupancy period of next selective contention period.
 3. Methodaccording to claim 1, wherein the access point transmit a beacon signalincluding an information about start period of the contention mediumoccupancy period to each station, whereby selective contention betweenthe stations is performed.
 4. Method according to claim 3, wherein thebeacon signal, the prescheduled medium occupancy period, and thecontention medium occupancy period are provided in turn in the selectivecontention period.
 5. Method according to claim 1, when a station issuccessful for a contention at the contention medium occupancy period ofthe selective contention period, a wireless medium occupancy reservationhaving a duration period for the contention successful station isprescheduled within a prescheduled medium occupancy period of nextselective contention period, then start period of a contention mediumoccupancy period of next selective contention period is moved forwardfrom the start period of the contention medium occupancy period of theselective contention period by the duration period.
 6. Method accordingto claim 1, when a first station is successful for a first contention atthe contention medium occupancy period of the selective contentionperiod, subsequently a second station is successful for a secondcontention after the first contention, a first medium occupancyreservation having a first duration period for the first station isprescheduled within a prescheduled medium occupancy period of nextselective contention period, subsequently a second medium occupancyreservation having a second duration period for the second station isprescheduled after the first medium occupancy reservation within theprescheduled medium occupancy period of next selective contentionperiod, then start period of a contention medium occupancy period ofnext selective contention period is moved forward from the start periodof the contention medium occupancy period of the selective contentionperiod by sum of the first duration period and the second durationperiod.
 7. Method according to claim 6, wherein the start period and theduration period of transmissions from the first and second stationsaccording to the scheduled wireless medium occupancy reservation arerecorded in both the first and the second stations.
 8. Method accordingto claim 1, wherein the station monitors condition of the wirelessmedium occupancy in the selective contention period, and records thecondition, then transmission timing is determined according to thecondition of the wireless medium occupancy recorded.
 9. Method accordingto claim 1, when the access point receives null packet transmitted atthe transmission timing according to prescheduled wireless mediumoccupancy reservation having a duration period for the station, theprescheduled wireless medium occupancy reservation will be cancelled,then start period of the contention medium occupancy period of nextselective contention period will be moved back by the duration period.10. Method according to claim 3, wherein the beacon signal furtherincludes information with respect to: (i) start period and end period ofselective contention period having the contention medium occupancyperiod and the prescheduled medium occupancy period of the selectivecontention period; and (ii) duration period of the selective contentionperiod.
 11. Method according to claim 10, wherein the beacon signalfurther includes information with respect to start period and durationperiod of prescheduled wireless medium occupancy reservation within theprescheduled medium occupancy period.
 12. Method according to claim 1,wherein the station transmits data stream having last packet includingreservation parameter for wireless medium occupancy reservation having aduration period in prescheduled medium occupancy period of nextselective contention period, the access point receives the reservationparameter included in last packet, wireless medium occupancy reservationfor the station will be prescheduled in prescheduled medium occupancyperiod of next selective contention period, then the start period of thecontention medium occupancy period will be moved forward by the durationperiod.
 13. A wireless network system comprising a plurality of stationsand an access point communicating with the stations via wireless medium,the access point comprising: a medium recorder unit which records: (i)start and end period of contention medium occupancy period in whichstations contend for wireless medium occupancy for a station to transmitdata stream, wherein the contention medium occupancy period is includedin a selective contention period; and (ii) start and end period ofprescheduled medium occupancy period in which wireless medium occupancyis prescheduled, and transmission is performed according to theprescheduled wireless medium occupancy, wherein the prescheduled mediumoccupancy period is included in the selective contention period; acontroller unit which preschedules wireless medium occupancy reservationhaving a duration period for contention successful station inprescheduled medium occupancy period, and moves forward the start periodof contention medium occupancy period of next selective contentionperiod by the duration period; a transmitter unit which transmits abeacon signal including information for start period of the contentionmedium occupancy period to the stations; and a receiver unit whichreceives data stream transmitted from the station, at least one stationcomprising: a receiver unit which receives the beacon signal includinginformation of the start period of the contention medium occupancyperiod transmitted from the access point via the wireless medium; atransmitter unit which transmits data stream via the wireless medium; amedium recorder unit which records transmission record; and a controllerunit which extracts the information of the start period of thecontention medium occupancy period from the beacon signal, and monitorscondition of wireless medium occupancy at every monitoring period amongthe start period and the end period of the contention medium occupancyperiod, then instructs the transmitter to transmit data stream when thecontroller unit confirms that wireless medium is not occupied.
 14. Anaccess point communicating with a plurality of stations via wirelessmedium, the access point comprising: a medium recorder unit whichrecords: (i) start and end period of contention medium occupancy periodin which stations contend for wireless medium occupancy for a station totransmit data stream, wherein the contention medium occupancy period isincluded in a selective contention period; and (ii) start and end periodof prescheduled medium occupancy period in which wireless mediumoccupancy is prescheduled, and transmission is performed according tothe prescheduled wireless medium occupancy, wherein the prescheduledmedium occupancy period is included in the selective contention period;a controller unit which preschedules wireless medium occupancyreservation having a duration period for contention successful stationin prescheduled medium occupancy period, and moves forward the startperiod of contention medium occupancy period of next selectivecontention period by the duration period; a transmitter unit whichtransmits a beacon signal including information for start period of thecontention medium occupancy period to the stations; and a receiver unitwhich receives data stream transmitted from the station.
 15. An accesspoint according to claim 14, when the receiver unit receives a nullpacket transmitted at the transmission timing according to prescheduledwireless medium occupancy reservation having a duration period for thestation, the prescheduled wireless medium occupancy reservation will becancelled, then start period of the contention medium occupancy periodof next selective contention period will be moved back by the durationperiod.
 16. A station communicating with an access point via wirelessmedium, the station comprising: a receiver unit which receives a beaconsignal including information of start period of contention mediumoccupancy period transmitted from the access point via the wirelessmedium, wherein in the contention medium occupancy period the stationcontends with other station for wireless medium occupancy to transmitdata stream; a transmitter unit which transmits data stream via thewireless medium; a medium recorder unit which records transmissionrecord; and a controller unit which extracts the information of thestart period of the contention medium occupancy period from the beaconsignal, and monitors condition of wireless medium occupancy at everymonitoring period among the start period and the end period of thecontention medium occupancy period, then instructs the transmitter totransmit data stream when the controller unit confirms that wirelessmedium is not occupied.
 17. A station according to claim 16, when thestation is successful for a contention at the contention mediumoccupancy period of the selective contention period, and acquires awireless medium occupancy reservation having a duration period for thecontention successful station, then the station extracts information ofstart period of the contention medium occupancy period of next selectivecontention period, and begins to transmit data stream at a time beforethe start period of the contention medium occupancy period by theduration period.
 18. A station according to claim 16, wherein the mediumrecorder unit records the medium record including condition of wirelessmedium occupancy in both the contention medium occupancy period and theprescheduled medium occupancy period of the selective contention period,wherein the controller unit calculates transmission timing at which thestation transmits data stream in the prescheduled medium occupancyperiod according to the transmission record.
 19. A station according toclaim 16, when first and second stations are prescheduled respectivelywithin the next prescheduled medium occupancy period, and the firststation's transmitter unit transmits a null packet which is a kind ofbroadcasting packet sent to all stations in order to release its ownprescheduled wireless medium occupancy, and the second station'sreceiver unit receives the null packet from the first station, then thecontroller unit of the second station realizes that the prescheduledwireless medium occupancy reservation for the first station iscancelled, and rearranges its transmission order of the second stationwithin the next prescheduled medium occupancy period by using the mediumrecord recorded by the medium recorder unit of the second station.